1. Field of the Invention
The present invention relates to an interchangeable lens that can be detachably attached to a camera body and that can carry out data communications with the camera body.
2. Description of the Related Art
A conventional SLR camera system, in which a photographic lens is interchangeable, is used by combining a camera body and an interchangeable lens selected from among various interchangeable lenses, and accordingly, each interchangeable lens incorporates a memory (lens memory) into which lens data inherent in the interchangeable lens is written so that the camera body reads out this lens data from the lens memory to use this lens data for controlling a photographic operation at a time of exposure. For instance, in conventional zoom lenses such as disclosed in Japanese Unexamined Patent Publications 2002-244188 (hereinafter referred to as Patent Document 1) and 2002-258380 (hereinafter referred to as Patent Document 2), lens data is written into memory by a paging method for each focal length step because the lens data needs to be changed according to variations in focal length caused by a zooming operation. Upon the focal length of the zoom lens being changed, a page corresponding to the changed focal length is detected by a zoom code output device and designated via hardware, and thereupon the camera body reads in the data in this designated page from the lens memory without concern for variations in focal length caused by a zooming operation.
Additionally, in a conventional camera system in which a photographic lens is interchangeable, the interchangeable lens incorporates a controller (CPU) in the case where sophisticated capabilities such as an AF capability and a zooming capability are incorporated in the interchangeable lens. This conventional type of camera system is disclosed in Patent Documents 1 and 2 and Japanese Unexamined Patent Publication 2003-35924 (hereinafter referred to as Patent Document 3).
However, a conventional communication device which carries out data communications with a lens memory cannot carry out communications with a lens CPU even if capable of reading in lens data written in a lens memory. Therefore, when the conventional communication device carries out communications selectively with the lens memory and the lens CPU, communication lines are switched (in a manner as shown in Patent Documents 1 and 2), or the conventional communication device carries out communications via the lens CPU at all times (in a manner as shown in Patent Document 3).
However, in camera systems, it is desirable for the number of communication lines and signals, for use in communication between a camera body and an interchangeable lens mounted to the camera body, to be as small as possible, and it is undesirable to add any extra communication lines or signals in order to ensure compatibility between the camera body and the interchangeable lens.
On the other hand, the greater the number of sophisticated features in the camera body and/or in the interchangeable lens, the greater the amount of data and the greater amount of data processing is required, which increases the necessity for the camera body to read a zoom code and a distance code from the camera body in a short period of time. Moreover, conventionally, a zoom code and a distance code are used solely for page swapping and that the camera body cannot read a zoom code and a distance code directly from the interchangeable lens.